44
Ind. Eng. Chern. Prod. Res. Dev., Vol. 17, No. 1, 1978
is essentially equivalent; both are somewhat better than the resin used for the formulations of Figure 3. The inhibitor package of formulation R is relatively ineffective: salt spray performance is roughly equivalent to that of formulation C. The inhibitor package of formulation 0, however, effectively slows the overall corrosion rate and reduces thereby the extent of alkali displacement. Failure is confined to within 1 mm of the scribe. Figure 5 presents results on a cathodically electrodepositable formulation. Little or no failure was observed with this material under the anodic, cathodic, and salt spray exposure tests used. The cathodic test results indicate that this resin is substantially more resistant to alkali displacement than the others included in this study. This is also reflected in the excellent performance in salt spray testing. The cathodically electrodepositable primer was clearly superior in corrosion performance to any of the anodically electrodepositable primers tested. Because of the excellent resistance of this resin to alkali displacement, it is not possible to assess from these tests the contribution of inhibitive pigments to primer performance. The performance of the sprayed film was slightly inferior to that of the electrodeposited film, indicating that the electrodeposition process plays only a minor role in determining corrosion performance. Conclusions Comparison of adhesion failure in conventional salt spray with results obtained using simple electrochemical test
methods allows evaluation of failure mechanisms and assessment of relative contributions of primer resin and pigmentation to overall corrosion performance. Evaluation of typical sprayed and electrodeposited primers on bare cold rolled steel indicates that adhesion failure under anodic conditions is minor and essentially independent of primer resin and pigmentation. Under cathodic conditions, adhesion loss is due to displacement of the primer by hydroxide ions. The extent of failure is greatly influenced by resin type. Dominant cause of failure in salt spray exposure is cathodic alkali displacement; corrosion inhibitive pigments improve performance in salt spray exposure by slowing the overall corrosion rate. Acknowledgment The authors acknowledgethe helpful cooperation of the Mt. Clemens Paint Plant of the Plastics, Paint and Vinyl Division, Ford Motor Company, in the preparation of primer formulations and test panels. Literature Cited Mayne, J. E. O., in "Corrosion", Vol. 1, 2nd ed, L. L. Shreir, ed, pp 15, 24-37, Newnes-Butterworths, London, 1976. Wiggle, R . R., Smith, A. G., Petrocelli, J. V., J. Paint Techno/., 40, 174 (1968).
Presented at the Division of Organic Coatings and Plastics Chemistry, 173rd National Meeting of the American Chemical Society, New Orleans. La. March 1977.
Advances in Anticorrosive and Antifouling Coatings N. A. Ghanem,* M. M. Abd El-Malek, and M. A. Abou-Khalil Laboratory of Polymers and Pigments, National Research Centre, Dokkl, Cairo, Egypt
M. M. El-Awady lnstitute of Oceanography and Fisheries, Kait Bay, Alexandria, Egypt
The reasons why the waters of Alexandria's eastern harbor present an interesting natural spot for testing underwater protection coatings are given. In continuation of a program for establishing structural properties relationships in anticorrosive and antifouling paints, well formulated protective systems are proposed encompassing up-todate international industrial trends of ingredients and techniques. In this paper, the merits of introducing lamellar aluminum in anticorrosive coatings, and a swellable nonhydrolyzable plasticizer in antifouling coatings of otherwise unified composition are domonstrated by long-term tests in natural environment. Correlation is given between the laboratory determined leached toxicity from the widely used cuprous oxide antifouling coatings and their effectiveness in preventing fouling in the natural environment. Laboratory as well as in-nature tests exhibit distinctive mechanisitic differences among formulations differing from each other only by the type of a minor constituent: the plasticizer.
Introduction The waters of Alexandria's eastern harbor provide a very interesting marine locality for testing underwater coatings systems (Abd El-Malek and Ghanem, 1975).The water is almost free of oil and toxic pollutants, rich in fouling organisms, 0019-7890/78/1217-0044$01.00/0
is always above 21 "C (except between December and March), and is constant in salinity at about 3.8%throughout the year. The pH value ranges from 8 to 8.3, which is similar to that of natural sea water in the open sea, and the dissolved oxygen content is very close to 3.5 mL/L except in the less warm 0 1978 American Chemical Society
Ind. Eng. Chem. Prod. Res. Dev., Vol. 17, No. 1, 1978
months when values near 6 mL/L are reached (Megally, 1970). Trials to establish underwater coatings systems which protect steel from corrosion and fouling for reasonable periods of time were carried out continuously during the last years in a specially built station floating in the vicinity of the Institute of Oceanography and Fisheries where the final preparations for the tests were performed. The trials were guided by the results of a systematic program of analysis and testing anticorrosive and antifouling coatings of various natures. The work included quantitative compositional characteristics of the respective coatings (Ghanem et al., 1971;Abou-Khalil et al., 1970) and the impact of the composition on the performance of the coating in the laboratory and in nature. For anticorrosive coatings, the laboratory tests included water uptake, electrode potential of coated steel, electrical resistance of the film, and pH of pigment extract after long periods of immersion (Ghanem et al., l971,1973a,b). For antifouling coatings of the copper type, the laboratory tests comprised accelerated glycine and acidalkali tests as well as normal leaching rate tests (Ghanem and Abd El-Malek, 1966; Hippi et al., 1962; Marson, 1964; U.S. Naval Institute, 1952). Laboratory tests on organometalliccontaining antifouling coatings which are gaining commercial importance are being performed using a newly developed neutron activation analysis technique (Ghanem et al., unpublished data). Incidentally, successful raft-testing results of antifouling paint compositions were already recorded (Abd El-Malek, 1972).The formulations were based on a vinyl copolymer and a high content of cuprous oxide; the films were free of fouling and retained their physical integrity after a period of 12 months of continuous immersion. But this result was still not very convincing from a practical point of view, since plastic sheets were used as substrates, whereas what is required by the Egyptian Standard Specifications (1966) is a paint system, applied on a steel substrate, that should provide protection from fouling and rusting for a minimum period of 6 months in local marine environment. Work recently published (Abd El-Malek and Ghanem, 1977; Abou-Khalil and Ghanem, 1977) revealed that certain compositional factors in both anticorrosive and antifouling paints greatly affect the efficiency of the protective systems. In anticorrosive coatings of the type containing anodic reaction inhibiting pigments, conclusions were reached that the pigment/binder weight ratio should not be less than 0.9, that 50% by weight of the total pigment should be any of seven inhibitive pigments examined (only three of which are suitable when cathodic protection is used), that the incorporation of the rosin-modified phenolic resins in vinyl binder improves the film properties but impairs the alkali resistance of the paint film, and that under cathodic protection the acidic binder content (acid value 20) should not exceed 10% of the total binder mixture. In antifouling coatings, 17 different formulations all depending upon cuprous oxide as toxin, a vinyl copolymer as stable binder, and rosin as soluble binder were tested in a raft on steel plates protected from corrosion by formulations selected from those mentioned in the above paragraph. While no single system satisfied the specifications requirements, important conclusions were reached (Abd El-Malek and Ghanem, 1977).To obtain any reasonable period of protection under the prevailing natural conditions, a high Cu20 content should be supplemented by a high ratio of rosin in the stable binder. Thus, the relatively more successful formulations were those containing 6555% CuzO with 27-36% of the total binder as rosin. It is noteworthy that the above series concentrated on finding out the role played by rosin in coatings containing
45
high ratios of Cu20. The reason for failure of fouling protection for the required period of time was believed to be the use of the wrong type of external plasticizer, which was of a nonhydrolyzable chlorinated paraffin type. In the present work, two minor modifications in the formulations are performed: one in the anticorrosive and one in the antifouling coating. In the anticorrosive coating, the pigment composition was modified by introducing aluminum powder, which is known for improving the impermeability to moisture and its ability to exclude ultraviolet light. The lamellar pigment particles have the property of laying themselves horizontly and concentrating in the outer part of the paint film. This “leafing” action, which may be due in part to the aluminum stearate film on the particles, serves to lengthen materially the path which the moisture must traverse to get through the film and may eliminate encountered blistering. (Abou-Khalil and Ghanem, 1977). In the antifouling coating, the nonhydrolyzable chlorinated paraffin plasticizer was replaced in one series by the hydrolyzable plasticizer tritolyl phosphate and in another series by the nonhydrolyzable but swellable plasticizer, polyvinyl methyl ether. The modifications created remarkable protection improvements which fulfilled the Egyptian Standard Specifications (1962,1966) requirements for the first time. Formulations Anticorrosive Formulations. As it is the aim in the present investigation to examine the value of introducing aluminum powder in the formulation, a typical already examined paint (Abou-Khalil and Ghanem, 1977) was used as reference. Its composition is given in Table I; its anticorrosive function may be ascribed to the presence of high content of the inhibiting pigment basic lead sulfate believed to act as an anodic passivator. The formulations containing aluminum powder were prepared and arranged in three series. Series 1 (Table 11) examines the effect of different binders on the efficiency of the paint. Series 2 (Table 111) examines the effect of introducing inhibitive pigment in the aluminum-containing paint. Series 3 (Table IV) examines the effects of some common inert pigments, extenders, and fillers on the paint efficiency. Antifouling Formulations. The antifouling paints formulated with nonhydrolyzable, hydrolyzable, and swellable nonhydrolyzable plasticizers are given in Tables V, VI, and VII, respectively. The individual paint compositions are given under serial numbers 1to 27. With each plasticizer nine formulations were made; each three of them have the same pigment/binder ratio of 3.5,4, and 4.5. The increase of the pigment/binder ratio was performed mainly through the increase of iron oxide and zinc oxide contents rather than through the increase of the content
Table I. Reference Anticorrosive Formulation without Aluminum Constituent Vinyl copolymer Chlorinated paraffin Rosin-mod. phenolic resin Phenolic resin TOTAL BINDER Basic lead sulfate Iron oxide Talc Barytes TOTAL PIGMENT Pigment:binder PVC
Amount 198 22 110 110
440 280 56 84 140 560 1.3:l
24
46
Ind. Eng. Chem. Prod. Res. Dev., Vol. 17, No. 1, 1978
Table 11. Anticorrosive Formulations with Aluminum and Different Binders AC no. Constituent Epoxy resin Hardner Vinyl copolymer Plasticizer TOTAL BINDER Aluminum Talc TOTAL PIGMENT Pigment:binder Constituent Chlorinated rubber Plasticizer Vinyl copolymer Coumarone-indene Plasticizer Vinyl copolymer Phenolic resin Rosin-mod. phenolic resin Plasticizer TOTAL BINDER Aluminum Talc TOTAL PIGMENT Pigment:binder
1
2
3
4
5
6
7
8
9
10
37 13
37 13
37 13
37 13
37 15
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
50 20 30 50
50 10 40 50
45 5 50 30 20 50
45 5 50 10
50
45 5 50 40 10 50
45 5
50
45 5 50 50
1
1
1
1
1
50 50 -
40 10
50
50
50 30 20 50
1
1
1
-
-
11
12
13
14
15
AC no. 16
37 13
37 13
-
-
-
-
-
-
-
-
-
22 25 3
22 25 3
22 25 3
22 25 3
-
1
18
19
20
21
-
-
-
-
22
25 3
-
-
-
-
-
-
-
-
50 50
50 20 30 50
40 50
1
1
1
1
50 30 20 50 1
-
50
50 40 10 50
50
50
50 30 20 50
1
1
-
50
-
-
-
40
17
-
50 50
20 30 50 1
22
-
-
50
22 15 10 3 50 50
-
10
-
-
22 15
-
22
15
15
10
10
10
50
3 50 30 20 50
3 50 20 30 50
3 50 10 40 50
1
1
1
1
Table 111. Anticorrosive Formulations with Aluminum and Different Inhibitive Pigments AC no. Constituent Vinyl copolymer Phenolic resin Rosin-mod. phenolic resin Plasticizer TOTAL BINDER Aluminum Talc Basic lead carbonate Basic lead sulfate Calcium plumbate Zinc phosphate Barium metaborate Basic lead silicochromate TOTAL PIGMENT Pigment: binder
22
23
24
25
26
27
22
22
15 10 3 50 30 5
22 15
22 15
-
22 15 10 3 50 30 5
22
15 10 3 50 30 5 15
3 50 30 5
-
-
15
-
-
-
15
-
-
-
-
-
-
-
50
50
50
1
1
1
-
10
15 10 3 50 30 5
10
3 50 30 5
15
-
-
-
-
-
15
-
50 1
50
15 50
1
1
-
-
Table IV. Anticorrosive Formulations with Aluminum and Different Inert Pigments. Extenders. and Fillers AC no. Constituent Vinyl copolymer Phenolic resin Rosin-mod. phenolic 1resin Plasticizer TOTAL BINDER Aluminum Talc China clay Baryte Titanium dioxide Micaceous iron oxide Iron oxide TOTAL PIGMENT Pigmenkbinder
28
29
30
31
32
33
22
22 15 10 3 50 35
22
22 15
22
22
15
15
10
10
10
3 50 35
3 50 35
3 50 35
15 10
3 50 35 15
15 10 3 50 35
-
15 -
15
-
-
-
-
15
-
-
50
50
50
50
50
15 50
1
1
1
1
1
1
Ind. Eng. Chem. Prod. Res. Dev., Vol. 17, No. 1, 1978
47
Table V. Antifouling Formulations with Nonhydrolyzable Plasticizer Constituent Vinyl copolymer Chlorinated paraffin Rosin-mod. phenolic resin Ester gum Rosin WW TOTAL BINDER Cuprous oxide Iron oxide Zinc oxide China clay Additives TOTAL PIGMENT Pigmenkbinder
1
2
3
4
127 12.5 22 25.5 33 220 724 25 14 16
127 12.5 22 25.5 33 220 645 99 19 16
127 12.5 22 25.5 33 220 567 103 93 16
115 11
20 24 30 200 744 26 13 16 1 800 4
1
1
1
780 3.5
780 3.5
780 3.5
AF no. 5
6
7
8
9
115
115
11
11
104 10
104 10
20 24 30 200 664
20 24 30 200 584 106 93 16
104 10 18
18
18
22
22 27
22 27
100
19 16
27 181
181
181
760 27 15 16
679 104 19 16
592 110 95 16
1
1
1
1
1
800 4
800 4
819 4.5
819 4.5
819 4.5
15
16
17
18
104 15
104 15 18 17 27
104 15
181
181
181
760 27 15 16
679 104 19 16
596
Table VI. Antifouling Formulations with Hydrolyzable Plasticizer Constituent Vinyl copolymer Tritolyl phosphate Rosin-mod. phenolic resin Ester gum Rosin WW TOTAL BINDER Cuprous oxide Iron oxide Zinc oxide China clay Additives TOTAL PIGMENT Pigment:binder
10
127 19 22 19 33 220 724 25 14 16
11
13
12
127 19
127 19
22
22
19 33 220 645 99 19 16
19 33 220 567 103 93 16
1
1
1
780 3.5
780 3.5
780 3.5
115 17 20 18 30 200 744 26 13 16 1 800 4
AF no. 14 115 17 20 18
30 200 664 100
19 16 1
800 4
115 17 20 18 30 200 584 106 93 16 1 800 4
18
17 27
18
17 27 111
95 16
1
1
1
819 4.5
819 4.5
819 4.5
Table VII. Antifouling Formulations with Swellable Plasticizer Constituent Vinyl copolymer Lutonal M40 Rosin-mod. phenolic resin Rosin WW TOTAL BINDER Cuprous oxide Iron oxide Zinc oxide China clay Additives TOTAL PIGMENT Pigment:binder
19 127 38 22 33 220 724 25 14 16
20 127 38 22 33 220 645 99 19 16
22
23
24
25
26
27
115
115 35 20 30 200 664
115 35 20 30 200 584 106 93 16 1 800 4
104 32 18 27
104 32 18 27
104 32 18 27 181 596
21
127 38 22 33 220 567 103 93 16
35 20 30 200 744 26 13 16
100
19 16
1
1
1
1
1
780 3.5
780 3.5
780 3.5
800 4
800 4
of the main toxin (CuzO) in order not to mask the effects created by the different plasticizers. However, the contents of CuzO with respect to total solids were kept a t the high copper content of the contact-leaching types of antifouling paints, Le., 58 to 76%.
Paint Application Steel plates 30 X 20 X 0.1 cm were cleaned in the usual way until a uniform shiny surface of the metal appeared. Several anticorrosive coatings were applied until a thickness of a t least 200 pm was obtained, allowing sufficient periods for drying between each coat. The edges were then protected by a twocomponent epoxy resin. One to two coatings of the antifouling paints were then employed to produce a thickness of a t least 80 pm. The plates were hung in frames each including one or two plates coated with nonantifouling paint to serve as blanks.
181
181
760 27 15 16
679 104 19 16
111
95 16
1
1
1
819 4.5
819 4.5
819 4.5
Testing The paint systems were immersed in the testing station (Abd El-Malek and Ghanem, 1975) in Alexandria harbor on May 24,1976. Periodic visual and biological examination and photographic recording of the condition of the plates were performed. A few days after the examination on Dec 9,1976, the station was hit by a sudden storm and sank. Much distortion occurred to most of the plates which made continuation of the exposure impossible. However, the rusting condition a t that stage was recorded by scraping and visual examination. The normal leaching rates of the antifouling paints were simultaneously determined and the test is continuing until the present date. The water temperature in the beakers during the test (Abd El-Malek and Ghanem, 1977) was always kept at 24 f 1 "C.
I Figure 5. Antifouling paint with swellable plasticizer: 176 days of immersion; B, blank plate; anticorrosives of Table I t AF no. 25 (Table VII).
I
I
01 I
30
60
90
120
150
180
210
210
270
ilML (DAYS1
Figure 8. Typical leaching rate experiments of antifoulings with * swellable plasticizer. Figure 7 records the leaching behavior of copper, for the same period of time, from paints also selected a t random from 0
30
60
90
120
150
180
210
210
270
300
TIME lMYS1
Figure 6. Typical leaching rate experiments of antifoulings with nonhydrolyzable plasticizer.
the rims. It must he noted that the condition of fouling on the plates increased remarkably after the third month of immersion. Much better results are obtained in the series shown in Figure 5 employing a swellable hut nonhydrolyzahle plasticizer. After a longer period of immersion, 176 days, the coating system is completely intact and fouling is either absent or a t a minimal level. Any fouled spot could he ascribed to some mechanical damage which occurred accidently during lifting and reimmersing the testing racks for periodic examination. Leaching R a t e Experiments. Lahoratory support to the above findings is provided from leaching rate experiments carried out simultaneously on the same paints (AF-No 1-27) tested in the raft. As already stated, the raft sank about 7 months after sample exposure; however, the laboratory leaching rate test is operational to the present date and will, hopefully, go on until the end. Figure 6 records the leaching behavior of copper for 10 months (last reading on March 9,1977) from paints prepared with chlorinated paraffin plasticizer. It can he shown that while the leaching of copper is satisfactory during the first 2 months, i t sinks quite rapidly afterward to values of 10 pgl (cm2day) or less, which is insufficient for a fouling rich environment such as that of the present investigation.
the series prepared with tritolyl phosphate as plasticizer. I t can he shown that although the leaching of copper is higher and is extended to a period of about 3 months, the leaching that follows is characterized by values very near the critical 10-pg line. The influence of the swellable plasticizer on the leaching rate is shown in Figure 8 which records high values for a much extended period of time; leaching rates higher than 15 pg/(cm2 day) are recorded 10 months after continuous immersion in tanks in the laboratory. The trend of the curves promises longer protection periods. The differences between the leaching behavior of three paints selected a t random, each containing one of the three different plasticizers, are clearly represented in Figure 9. The hydrolyzable plasticizer allows initially higher leaching rates than the two other plasticizers hut only for a period of 2 to 3 months after which the leaching rate falls to somewhat critical values which might allow scattered settlement. The nonhydrolyzahle plasticizer, on the other hand, does not allow sufficient leaching after a period of not more than 1or 2 months; an otherwise proper formulation is thus wasted, particularly under prevailing warm and fouling-rich conditions. The for. mulation which gives optimum behavior is that containing an unconsumahle but swellable plasticizer which allows opening of the structure without unnecessary loss of active ingredient; formulations with Lutonal exhibited a greenish appearance which increased in intensity along the leaching rate experiment. This is most prohahly basic copper carbonate retained in voids created as the plasticizer swells. Conclusion Raft testing in a natural environment which combines
50
Ind. Eng. Chem. Prod. Res. Dev., Vol. 17,No. 1, 1978
I *Ot
B \
Acknowledgment The authors are grateful to many companies for their cooperation in providing samples and instructions. We are particularly grateful to BASF, AG Ludwigshafen, for their continuous supply of raw materials of their own and other companies' products, and for useful discussions and technical information, particularly with Dr. Neubert, Dr. Brussmann and Dr. Morcos of ANETA-LARO department. The work represents part of the activities under contract No. 0001475-C-1112 between the National Research Centre of Egypt and the Office of Naval Research of the Department of the Navy of the U.S.A.
t
60-
.
v
a b
17
I
VI 0-0
- e
30
63
90
120 '50 TIME (DAYS)
183
210
210
270
303
Figure 9.
Comparison between leaching rates o f antifoulings w i t h different plasticizers: X, w i t h nonhydrolyzable AF no. 6 ; 0 ,w i t h hydrolyzable AF no. 17; 0 , w i t h swellable AF no. 21.
Literature Cited Abd El-Maiek, M. M., Ph.D. Thesis, Faculty of Science, Cairo University,
1972. Abd El-Malek, M. M., Ghanem, N. A., J. Paint Techno/., 47 (608),75 (1975). Abd El-Malek, M. M., Ghanem, N. A,, "Proceedings of the Fourth International Congress on Marine Corrosion and Fouling, Juan-les-Pins, France, June
1976", 1977. Abou-Khalil, M. A., Abd El-Malek, M. M., Ghanem, N. A,, Paint Manuf., 40 (lo),
32 (1970).
rather severe climatic conditions with nontoxic pollution provides valuable information as to the efficiency of underwater protective systems. In anticorrosive paints, incorporation of lamellar aluminum in formulations based on a vinyl copolymer as binder provides better protection than when inhibiting pigments of the anodic passivation class are used without aluminum. In antifouling paints, a swellable but nonhydrolyzable plasticizer is superior to both nonhydrolyzable and hydrolyzable counterparts in regulating toxin release and allowing retention of surface copper in the form of basic copper carbonate.
Abou-Khalii, M. A., Ghanem, N. A., "Proceedings of the Fourth International Congress on Marine Corrosion and Fouling, Juan-ies-Pins, France, June
1976",1977. Egyptian Standard Specifications No. 197,1962,and 765,1966.The Egyptian General Authority for Standard Specifications, Cairo, Egypt. Ghanem, N. A., Abd El-Maiek, M. M., J. Chem. Egypt Arab Rep., 9, (3),377
(1966). Ghanem, N. A,, Abou-Khalii, M. A,, Farbe & Lack, 79 (3),201 (1973a). Ghanem, N. A., Abou-Khalii, M. A., Farbe & Lack, 79 (ll),1041 (1973b). Ghanem, N. A.. Moustafa, A. B., Abou-Khaiii, M. A,, Farbe& Lack, 77 (lo),961
(1971). Hippe, Z., Jedlenski, Z., Korat, J., Uhacz, K., J. Oil Colour Chem. Assoc., 45,
653 (1962). Marson, F., J. Oil Colour Chem. Assoc., 47, 323 (1964). Megally, MSc. Thesis, Faculty of Science, Alexandria University, 1970. Woods Hole Oceanographic institution, "Marine Fouling and Its Prevention", U S . Naval Institute, Annapolis, 1952.
Empirical or Scientific Approach to Evaluate the Corrosion Protective Performance of Organic Coatings W. Funke* and H. Haagen Forschungsinstitut fur Pigmente und Lacks, 0-7000Stuftgart 1, West Germany
Water and oxygen permeability of organic coatings and their adhesion when exposed to high humidity are proposed as basic properties to estimate the corrosion protective performance. Contrary to the visual criteria commonly used in conventional corrosion testing, these film properties provide information on how to improve the corrosion protective performance of organic coatings. A method of estimating adhesion of the humid film on a steel surface is described and the influence of some experimental variables on oxygen permeability is discussed.
Introduction There are not many subjects of paint research that have been more extensively studied over many years than the evaluation of corrosion protection by paint films. Despite these manifold efforts and the fact that the fundamentals governing corrosion under a paint film have been known for a long time the testing of the corrosion protective property still remains on a remarkably primitive level. Salt spray tests, exposure to sulfurous dioxide, water, or water vapor a t elevated temperatures, or water condensation tests are com0019-7890/78/1217-0050$01.00/0
monly used and results obtained by them often differ significantly from practical behavior. It is not surprising therefore, that practical exposure tests are still considered to be the most reliable means to recommend a paint or coating to a customer for special applications. Irrespective of whether a laboratory or practical corrosion test is considered, the testing results are mainly based on the appearance of the samples after exposure. This means that the evaluation is based upon the result and not on the properties which are responsible for good or poor protective be0 1978 American Chemical Society
